What is Animation Nodes addon used for?
The Animation Nodes addon (AN) is a "Node based visual scripting system designed for motion graphics in Blender."

It allows the creation of procedural animations. Furthermore, it can achieve many effects that are otherwise only possible through programming.

To get a better impression of what is possible, check the showreels for 2015, 2016 and 2017.

Download Animation Nodes Addon.

You can find the official documentation here. It also includes a list of most of the tutorials creators.

Check the official Blender Artists thread where the community collaborate, share their work and provide information about AN.